1. Field of the Invention
The present invention relates to a printing apparatus, such as a laser beam printer, that generates bit map data from print data which are input from the outside and prints the data, and to a memory medium that is employed to store a control program.
2. Related Background Art
A page printer, such as a laser beam printer, must store an output image for one page in a bit map memory. To do this, there are a full paint method, which requires a full page bit map, and a banding method, by which a band bit map covering a fractional portion of a page is employed to generate an image for one page.
The full paint method requires a bit map memory for one page, and data to be printed are transferred to a printing mechanism (a printer engine) after an image is generated on a bit map memory. According to this method, for example, a bit map memory of about 8 MB is required for an A3 size sheet at a resolution of 600 DPI. However, since an output image for one page can be generated even for a great amount of data, or for data that require a long time for image generation, the print output of input data is ensured.
According to the banding method, data to be printed for one page are stored as intermediate data in the apparatus. A bit map memory for a fractional portion of a page is used as a ring buffer (band buffer), and the generation and the transfer of an output image must be controlled by employing a synchronization signal that is output by a printing mechanism (printer engine).
Compared with the full paint method, the banding method can be performed with a smaller memory capacity, and as the generation (rendering) of an output image and a transfer of the output image to the printing mechanism (printer engine) can be performed at the same time, the processing speed is increased.
Conventionally, in the full paint method, a bit map memory for one page is required, and in the banding method, a bit map memory for a fractional portion of a page is required. The capacity of a bit map memory, therefore, increases in proportion to the resolution of a printing apparatus and to the size of the sheet that can be handled.
Compared with the full paint method, the conventional banding method must store data for a single page that is to be printed as intermediate data in the apparatus. Therefore, when the intermediate data for one page can not be stored, printing can not be performed.
Further, an image must be generated and transferred in consonance with a synchronization signal from the printing mechanism (printer engine). However, because of the enormous amount of intermediate data, an output image can not be generated within a determined time period, an overrun occurs, and as a result, printing can not be performed.
As is described above, although the conventional banding method can reduce the memory capacity that is required for a bit map memory, with this method, print data that are input sometimes can not be output.